Hip fractures are the most common fracture of older age. Although the age- specific hip fracture rate in men is approximately half that in women, the risk of hip fracture in men is till substantial; the cumulative incidence is 17% by the age of 90. Very little is known about the causes of osteoporosis and osteoporotic fractures in men. No etiologic study of hip fracture in men has been conducted in the United States. The objective of this case-control study is to identify specific, important risk factors for hip fracture in men by comparing men with hip fracture to age-matched male controls. The study is directed towards evaluating the relative importance of factors associated with osteoporosis vs factors associated with the risk of falling. A secondary goal of the study is to compare the risk factors identified in men with those identified in women from our present case-control study of hip fractures in women. In addition, we now propose to include a laboratory assessment of gonadal function. We plan to recruit 300 men 45 years and older with a first hip fracture admitted to one of 30 participating hospitals in Philadelphia and New York City. Hospitalized controls, 150 from each site, will be matched by age and hospital. In addition, 150 community controls from each site will be selected either through random digit dialing (for those under 65 years of age) or from among Medicare enrollees. Information about previous dietary habits, exercise, medical and surgical illnesses and medications, as well as demographic and social factors, and the circumstances of the trauma resulting in hip fracture will be obtained from personal interview and medical record review. Laboratory assessment will include an evaluation of total and free testosterone as well as related sex hormones. Univariate analysis, including calculation of odds ratios with confidence intervals, will be followed by stratification and multiple logistic regression, enabling us to evaluate the importance of each variable while adjusting for the others as confounders. The important factors will be combined into a clinically useful index to test as a predictor of increase risk for hip fracture among men. This research, involving experienced investigators who have been collaborating on a case-control study of women with hip fractures, should contribute significantly to our understanding of the causes of hip fractures in men, and ultimately, its prevention.